1. Field of the Invention
The present invention relates to a projector such as a liquid crystal projector for displaying images formed by light emitted from a discharge lamp onto a screen. More specifically, the invention relates to the control of the rotation of a cooling fan in a standby mode in which images are not projected on the screen.
2. Description of the Related Art
A known discharge lamp used as a light source of a projector cannot be turned on immediately after it is turned off. The discharge lamp can only be turned on again one to one and a half minutes after the discharge lamp has been turned off when the temperature of the discharge lamp is sufficiently reduced. When a projector is used in a presentation during a meeting, it might be turned off for a short period of time during a discussion not requiring an image to be projected. Once the discharge lamp is turned off, it cannot be turned immediately back on again to project the image. To turn on the discharge lamp again, the operator has to wait for a period of time. This waiting time causes inconvenience to the operator.
Moreover, when the projector is not required to project images (i.e., when the projector is in standby mode), maintaining the supply of electric power to the discharge lamp at the same level as in a normal mode in order to maintain the discharge state of the discharge lamp so that the discharge lamp continues to be lit is not only wasteful but also shortens the lifespan of the discharge lamp.
Accordingly, Japanese Laid-Open No. 10-239767 discloses a projector having a discharge lamp that shuts off the path of the light emitted from the discharge lamp with a cap and preventing the discharge lamp from going off by supplying up to 50% less electric power. Moreover, Japanese Laid-Open No. 2001-326086 discloses an image apparatus that allows electricity to be conserved by reducing the amount of electric power supplied to the discharge lamp depending on the image being projected.
A lighted discharge lamp in a normal mode continuously generates heat and reaches a high temperature. In addition, the temperature of an optical system (image projecting means) for projecting an image on a screen by the light irradiated from the discharge lamp becomes high. The high temperature of the discharge lamp and the optical system increases in proportion with the amount of electric power supplied to the discharge lamp. Once the temperature exceeds a predetermined temperature, the lifetime and performance of the discharge lamp and the optic system become degraded.
For this reason, a cooling fan is typically used for cooling the discharge lamp and the image projecting means. The cooling ability of the cooling fan can be controlled by changing the rotational speed of the fan. In this way, the rotational speed of the cooling fan is controlled so that the temperatures of the discharge lamp and the image projecting means do not exceed a predetermined temperature while the lighted discharge lamp is in the normal mode. There are also known projectors in which the rotational speed of the cooling fan is reduced in the normal mode and the amount of electric power supplied to the discharge lamp is reduced to conserve electricity.
In known projectors, however, the cooling fan is not turned off in the standby mode while the discharge state of the discharge lamp is maintained and the amount of electric power supplied to the discharge lamp is reduced. When the cooling fan is rotating, it generates noise. The noise of the cooling fan is particularly disturbing if the cooling fan keeps rotating when the projector is switched from the normal mode to the standby mode to have a discussion during a presentation.